Comparative chloroplast genome analysis of two Desmodesmus species reveals genome diversity within Scenedesmaceae (Sphaeropleales, Chlorophyceae)

Desmodesmus (Sphaeropleales, Chlorophyceae) is a genus of freshwater green algae widely distributed in aquatic ecosystems and known for its potential in biotechnology and bioremediation. We present the complete chloroplast genome sequences of two Desmodesmus species, D. hystrix and D. perforatus. Comparative analysis revealed significant differences in their quadripartite structures, particularly in the lengths of the small single copy regions. We observed variations in G + C content across genomic regions, with inverted repeat regions showing a higher G + C content. Microsatellite analysis revealed that A/T mononucleotides were the most abundant type, while dispersed repeat analysis suggested a potential link to expansion of the single-copy region in D. perforatus. Gene annotation, codon usage analysis, and comparison of genome rearrangement highlighted both similarities and differences between the species. Nucleotide diversity analysis revealed higher variability in intergenic regions than in coding regions, with IR regions displaying relative conservation. Comparative analyses of genomes and IR border arrangements demonstrated that the Desmodesmus species exhibit substantial differences in genome structure and gene arrangement among Scenedesmaceae. Phylogenetic analysis, based on 51 single-copy genes from 34 species of Sphaeropleales provided additional information about phylogenetic relationships within Sphaeropleales. These findings contribute to our understanding of comparative plastid genomics in green algae.